This invention relates to a shock absorbing cushion for athletic and industrial gear and footwear. More particularly, this invention relates to a shock absorbing cushion comprised of a sealed elastomeric envelope enclosing a compressible material and a fluid, wherein the compressible material is secured to the elastomeric envelope by a plurality of filaments, or a plurality of tensile elements forming the inner surface of said envelope material, and securely imbedded in said compressible material so as to substantially impede delamination between said envelope and said compressible material.
The cushion is particularly well suited to absorb the impact experienced in athletic endeavors and effectively return energy to the athlete. More particularly, the cushion is well suited to the intense and repetitious impact which occurs in short intervals during athletic activities. Throughout the specification, numerous references will be made to use of the cushion as a portion of the sole of athletic footwear; however, it should be realized that the inventive cushion can be beneficially incorporated into various types of footwear including, but not limited to, dress shoes, boots, sandals, etc. In addition, the new cushioning device can provide protection in many types of athletic equipment where these unique cushioning and dynamic characteristics would be beneficial such as football, soccer, baseball, knee, leg, shoulder, neck and arm pads, saddles, helmets, gloves, seat cushions, etc.
A great many shock absorbing devices exist in the footwear art to absorb the shock of foot strike. One common approach to impact absorption has involved using blocks of a compressible padding material. For example, shoes have been constructed with cotton padding, horsehair padding, rubber, plastic foam, and the like. In these shoes, the inherent resilience of the compressible padding material is used to absorb and disperse impact. However, these materials are relatively inefficient in their ability to return energy to the shoe wearer and after repeated use become compacted and lose their cushioning properties. Furthermore, on severe impacts, unless a relatively thick block of compressible padding is used, these designs experience full compression or "bottom out" quickly which results in severe impact stress on the wearer's body. When made thicker to avoid this problem, the compressible padding material becomes cumbersome and heavy and can interfere with the design of the footwear and in an athlete's performance. In addition, when the padding material is thick, instability may be encountered.
Within the grouping of cushions constructed of compressible padding materials, foam inserts are preferred in athletic footwear because of their light weight and relatively favorable cushioning characteristics. Notwithstanding the superiority of foam within the compressible padding material group, it has been found that the cellular structure of a foam insert degrades with time and cyclic loading, resulting in collapse of the cell walls, and the corresponding rapid reduction in the cushioning characteristics of the insert. On the other hand, as opposed to the fluid inserts discussed below, foam and other compressible materials are not subject to instantaneous failure.
To improve the characteristics of footwear cushions comprised of compressible padding materials, shock absorbing devices have been developed which are based on the properties of fluids. Usually, these cushioning devices are comprised of a fluid encased within an elastomeric material. In the case of compressible fluids (ex. gasses), these devices rely primarily upon the compression of the enclosed fluid to provide the desired shock absorbance. In the case of incompressible fluids, cushioning is provided primarily by the flow of the fluid and/or the expansion and contraction of chamber walls housing the fluid. In addition, there are devices based on the combination of compressible and incompressible fluids.
It is believed that fluid filled cushioning inserts provide superior overall cushioning and performance characteristics as compared to cushions constructed of foam and other compressible padding materials. Particularly, energy return is generally believed to be more efficient in fluid filled devices, and there is likely to be an increase in the longevity of the device. Moreover, the cushioning activity of fluids does not degrade with time. Only when the elastomeric material containing the fluid experiences structural failure or puncture does the device cease to perform at a high level. Accordingly, it is essential in compressible and incompressible fluid containing cushions to provide a long-lived elastomeric encasement. However, two competing design factors complicate this endeavor.
First, a device having exceptional longevity can be achieved with a thick, strong, and durable elastomeric envelope. However, a thick envelope mitigates the benefits of fluid cushioning because the characteristics of the fluid are replaced and masked by those of the elastomeric material. Accordingly, it is desirable to have a thin walled envelope to obtain the maximum benefits of fluid cushioning. Unfortunately, a thin, flexible envelope may have too short of a lifespan before rupture.
Second, the competing interests of intrusive versus unobtrusive envelopes arises when a particular shaped cushion is desired. Moreover, fluids do not have an inherent shape. Therefore, the elastomeric material must assert shaping forces on the fluid. Obviously, a thick, strong elastomeric envelope can easily form complex shapes; however, the characteristics of the fluid medium are sacrificed. Of course, to highlight the desirable attributes of the fluid, the elastomeric member can be made thin and flexible; however, control of fluid flow and/or compression are all sacrificed.
As indicated above, considerable difficulty has been experienced in providing shaped, fluid filled cushions, particularly pressurized cushions, with a flat or smoothly contoured surface. One very successful solution to this dilemma is provided in U.S. Pat. No. 4,219,945 wherein a multichambered pressurized gas-filled elastomeric envelope is encapsulated in a visco-elastic foam. In this invention, the foam acts as a medium between a foot and the cushion and provides a smooth intermediate surface. Moreover, a cushion is formed of rounded tubular chambers of a thin and unobtrusive elastomeric material to provide exceptional fluid support. The cushion is then encapsulated in foam to fill the peaks and valleys and provide a specifically shaped cushion with a long life.
Notwithstanding the success of foam encapsulated gas-filled cushions, a desire persists to provide advancements thereon. In this regard, efforts have been made to provide a footwear cushioning device which provides the superior shock absorbing performance of fluids in combination with the complex shape and anatomic support obtainable via pad-type cushions. U.S. Pat. Nos. 4,874,640 and 5,083,361 are relevant endeavors into this type of cushioning device.
U.S. Pat. No. 4,874,640 describes a composite cushion comprised of a flexible plastic enclosure forming an internal cavity. The enclosure is generally impermeable to air and generally filled with a fluid that can be pressurized. The composite also includes a compression, impact absorbing foam core glued or bonded on its external surfaces to the internal surface of the plastic enclosure. The patent also suggests reinforcing the internal foam cushioning member by including filaments, fibers or fabrics to the integrating matrix of the foam core. Although initial cushioning is achieved with this design, it is believed that rapid delamination between either the reinforced or non-reinforced foam core and the external flexible plastic material can occur. This delimitation is a possible cause of an aneurism and/or instability.
U.S. Pat. No. 5,083,361 describes a pressurized gas inflated hermetically sealed barrier securely bonded on its inner surface to a double walled fabric structure. The double walled fabric structure is comprised of a first and second outer fabric layer spaced apart in a facing relationship yet interconnected with drop threads. The drop threads function essentially as tension members to position the opposing gas barrier surfaces in a precise geometric relationship from one to the other. In general, the interconnected fabric layers are connected to distal interior surfaces of the elastomeric material via a coupling material which penetrates and bonds to the fabric layers. This device has found significant commercial success. However, this device is relatively complex and expensive to manufacture. In addition, it should be noted that this device is inoperable as a cushion subsequent to a rupture or leak in the elastomeric barrier member.
Accordingly, the art is in need of a relatively inexpensive, long-lived, easy to manufacture, fluid containing cushioning device with controlled shape and cushioning characteristics. A particularly attractive means of achieving this end is the effective combination of fluid filled cushioning characteristics with the stability and reliability of compressible padding materials.